First of all, the entire atmosphere of Five Nights at Freddy's 4 is so much more dark then the rest of the series. You feel helpless as you crawl around your room, holding doors shut as monsters knock on them from the other side. Perhaps one of the worst feelings is when you catch from the corner of your eye your closet door moving. You move over to check it out and this greets you.
"Haha! What a great time I'm having! Video games are fun!" You think as you hastily smash your computer into a thousand pieces with a hammer and never look back.
Check out this video by AlleyoBells to get a true feeling for Foxy's mind games.